Dental restoratives are well known in the art and include for example, crowns, inlays, onlays, veneers, and fillings. Restorative materials are those utilized in repairing a damaged tooth, or in replacing an entire tooth. When repairing a damaged tooth, it is desirable not only that the tooth be returned to a useful state, but that it also be returned as close as possible to its natural aesthetic state, such that the color and appearance of the restored tooth blend in with the surrounding natural dentition.
Dental restorations are typically prepared according to two different techniques: (1) in situ or direct restorations, wherein the restoration is fabricated directly in the patient's mouth; and (2) indirect restorations, wherein the restoration is fabricated directly in a dental laboratory and subsequently communicated to the dental practitioner for placement in the patient's mouth. Direct restorations typically involve issues such as repairing a cracked tooth, treating a tooth for decay or filling in a space between adjoining teeth. Indirect restoration techniques are typically employed for more complex dental repairs, such as, for example, the replacement of a complete tooth. Indirect restorations are typically fabricated from ceramics or porcelains and involve the build-up of sequential layers of material. While indirect techniques are inherently more expensive, time consuming and require a greater level of technical expertise than direct placement techniques, they allow for a higher degree of aesthetic precision and typically provide a very natural looking restoration.
In a typical direct restoration, the tooth to be restored is initially treated by removing the decayed or damaged material and then the removed portion is restored with a dental restorative material. Conventional restorative materials include dental amalgams or metal alloys; flowable dental composites, such as those described in U.S. Pat. Nos. 3,066,112; 3,179,623; and 4,744,759 to Bowen; and condensable dental composites, such as those described in U.S. Pat. Nos. 4,381,918 and 4,392,828 to Ehrnford; U.S. Pat. No. 4,952,530 to Brosnan et al; U.S. Pat. No. 5,621,035 to Lyles et al.; and U.S. Pat. No. 6,013,694 to Jia et al. U.S. Pat. No. 6,300,390 to Angeletakis describes resin-based dental restoratives incorporating uniformly dispersed submicron sized reinforcing particulates and published United States Patent Application No. 2003/0175660 to Yin et al, describes a restorative composite including a spherical or sub-micron size filler bound together by a polyurethane dimethacrylate ester oligomer.
Dental restorative composites are typically dispersions of micro sized glass filler particles in a methacrylate-type monomer resin. Splintered, pre-polymerized particles or ground suspensions of silica in pre-polymerized dental resins, may also be used. Additives such as pigments, initiators and stabilizers may be included in these types of composites. Flowable dental composites are typically a reinforcing particulate inorganic filler bound together by a polymeric matrix. One commonly used flowable dental composite is a mixture of an organic polymer known as bisphenol-A-glycidyl methacrylate (Bis-GMA) and inorganic particles such as quartz, borosilicate glass, and lithium aluminum silicate. Typical condensable dental composites include various other alternative inorganic filler materials in a polymer matrix.
Due to their metallic appearance and low adherence to natural tooth structure, the growth of amalgams in dental restorations has remained flat with increasing growth in current dental practices typically utilizing various light-curable dental composites for fabricating restorations. In addition to being durable and wear resistant, dental composites are readily adaptable to coloring and can therefore provide a more natural looking restoration.
Conventional composite placement techniques for direct restorations typically include the steps of:                cleaning the tooth and while moistened, evaluating the overall shade/color appearance;        preparing the area for restoration, i.e., removing decayed/damaged enamel and dentin;        applying a bonding agent to the prepared area;        selecting correspondingly-colored dentin and enamel restorative materials, respectively;        applying the colored dentin material to restore the dentin layer;        applying the colored enamel material to restore the enamel layer; and        finishing and polishing the restoration.        
Optional steps might include applying a flowable composite prior to applying the colored dentin material, in order to fill in any voids or irregularities that may exist in the floor of the restoration area, or applying special effects to the restoration prior to finishing and polishing.
One of the most exacting and time consuming aspects of dental restorations, whether involving direct or indirect placement techniques, is that of properly matching the color of the restoration to that of the original tooth. In the context of clinical dentistry, the term “color” involves three discrete concepts: hue, chroma and value. Hue is the dimension of color that enables us to distinguish one family of color from another; chroma defines the relative intensity of a particular color, i.e., the more intense a color is, the higher its chroma level; and value describes the relative whiteness or blackness of a particular color, i.e., the brighter the color, the higher its value. In addition to these concepts, characteristics such as opacity, fluorescence, and translucency may also be considered during a dental restoration.
To aid in the determination of tooth color, a dental practitioner will often utilize a dental shade guide or other such similar device, to evaluate the color characteristics of the tooth. A typical dental shade guide has a base supporting a plurality of tabs or other indicia, each of which corresponds to a different color. A given guide may include a number of sets of tabs, one representing standard tooth colors, one representing standard dentin colors and one representing standard enamel colors. The colors are typically defined according to the CIE L*a*b* system wherein “L” refers to value (black is 0 and white is 100), “a” is a measurement on the red to green scale, and “b” is a measurement on the blue to yellow scale (Bilmeyer, F. W., Principles of Color Technology, 2nd ed., John Wiley, 1981).
Conventional shade guides are disclosed, for example, in U.S. Pat. No. 6,315,554 to Coste et al. and U.S. Pat. No. 6,030,209 to Panzera et al and published United States Patent Application Nos. 2003/0124481 to Zun; 2002/0081547 to Kerschbaumer et al.; and 2002/0064750 to Morris et al. Commercially available shade guides include Vitapan Classical™ (formerly, Vita-Lumin™ Vacuum Shade Guide), Vitapan 3-D Master™ (Vident, Brea, Calif.), Bioform™ and TruMatch™ (Dentsply International, Inc., Milford, Del.)
Conventional restoration techniques utilize a philosophy that both the dentin and enamel layers of teeth possess a color or shade which influences the overall color and appearance of the tooth. Standard shade guides categorize these colors into four basic groups: A, B, C, and D. In addition, each group may itself be internally categorized to include shades that add further characterization to restorations. Darker shades, for example, have been developed for older patients and bleach shades have been introduced in response to an increased use of whitening agents. In practice, the practitioner first chooses the color tab that most closely matches the overall color of the damaged tooth. The correspondingly-colored dentin and enamel restorative materials are then prepared and placed on the tooth. Thus, the color of the finished restoration will result from a combination of the colors of the dentin and the enamel restorative materials.
One drawback of this technique is therefore, the high level of skill and effort required to assure that the colored dentin and enamel materials, when combined, create the appropriate color result so that the restoration blends in with the surrounding dentition. As a result, although conventional tooth-colored composite placement techniques provide restorations that are much more aesthetically appealing than had previously been achieved with amalgams, for example, improved techniques continue to be sought. Direct placement techniques that provide a restoration having the aesthetic properties of an indirect ceramic restoration would be highly desirable. The principles of the present invention provide such techniques.